Python makes a pretty nice interactive calculator. You can do the other way around, too, with the builtin function bin(x). (And there are also hex() and oct() builtins, if you also need to go back ...

The table below shows the binary-to-decimal-conversion of the value of 500: Thus, 500 10 = 111110100 2. Or, on a digit by digit basis in base 2: 500 = (256 + 128 + 64 + 32 + 16 + 0 + 4 + 0 + 0) There ...